Mechanisms of Anion Transport in Salivary Glands The quality of life for millions of Americans is adversely affected by salivary gland hypofunction resulting from xerogenic medications, Sjogren's syndrome, radiation therapy, or systemic diseases. Given the vital role of transepithelial CI" movement in salivary gland secretion, perturbation of CI"transporter function is likely to be involved in many such conditions. The development of interventions to improve or restore function for these individuals therefore requires a thorough understanding of CI"transporter physiology. Salivation is a two step process. Initially, acinar cells secrete an isotonic, plasma-like fluid, and duct cells subsequently modify this primary secretion to conserve NaCI. Fluid secretion and NaCI reabsorption are dependent on the activation of both CI" channels and CIVHCOs" exchangers to generate transepithelial CI" movement. The general biophysical properties of these different classes of CI"transporter proteins are known in salivary gland cells, however, major gaps exist in our understanding of the genes involved as well as the relative contribution of each CI"transport mechanism to the overall secretion process. Thus, to verify and refine our understanding of the function of these proteins, Aim 1 will directly test hypotheses as to which CI" transport proteins are essential for in vivo fluid secretion through the study of animals where the functional expression of a specific gene has been disrupted. Using a high-throughput proteomics approach, Aim 2 will generate a comprehensive list of the ion transport proteins in salivary cells, including which of the Clca and Best Ca2+-activated CI" channels target to the plasma membrane. Biochemical and functional studies proposed in Aim 3 will test whether the CIVHCOy exchanger Ae2, which is critical to the fluid secretion process, is part of a regulatory "HCO3" transport metabolon." This multidisciplinary approach will define the essential CI" transport mechanisms involved in the production of saliva, which is necessary for addressing the challenge of treating salivary gland dysfunction.